The present invention generally relates to an apparatus for testing electronic components. The apparatus is particularly adapted for testing electronic components useful in high temperature environments.
Engineers are continually finding new applications for electronic components. Increasingly, these applications require electronics to operate under demanding environmental conditions, such as elevated temperatures. For instance, automobiles frequently utilize electronic circuits to monitor or control a number of the operating parameters of the engine, as in the case of electronic ignition systems. These circuits are generally located under the hood of the vehicle adjacent the engine where the ambient temperature can be rather high, often exceeding 100.degree. C. If such a component were to fail under operating conditions, it may well render the entire vehicle inoperable.
In order to increase the reliability of products incorporating such components, electronic systems are frequently tested as part of a quality control program before they are installed. The testing may be performed on each component or only on a representative sample of a larger batch of components to estimate the overall quality of the batch. The former approach is preferred because any component which fails the test can be eliminated, preventing the incorporation of a faulty component into the finished product. However, this extensive quality testing can be unduly expensive to carry out. In order to test components which will be placed in elevated temperature environments, it is necessary to test the components at high temperatures, such as in an oven, to simulate actual operating conditions. Providing such an environment can significantly add to the cost of a quality control program. Accordingly, it would be useful to have an efficient, economical process for testing a large number of electronic components at elevated temperatures.
Currently, an elongate oven having an electrical power supply is utilized to test electronic components, with the oven providing an elevated temperature environment in which the testing is carried out. The components are commonly placed on a generally horizontal conveyor belt or the like for transportation through the oven and are supplied with electricity as they are transported. In order to ensure a dwell time in the oven sufficient to heat the component to the desired temperature and monitor its behavior at that temperature, the ovens tend to be long and flat, taking up a great deal of valuable floor space in a factory.
The loading and unloading of the components from the conveyor system commonly takes place outside of the heated environment of the oven. The components remain on a portion of the conveyor which extends past the end of the oven until they have been cooled by the ambient air sufficiently to allow them to be removed. Not only does this further increase the floor space required for the system, but it also decreases the efficiency of the oven because the heat radiated by the components as they cool is lost to the environment. Additionally, the components will experience thermal shock as they enter and exit the heated oven unless intermediate temperature zones, commonly requiring separate control equipment, are provided at each end of the oven.
As noted above, electricity is applied to the component as it passes through the oven. The component usually is attached to an electrical connector which is connected to a power supply. The electrical connector may be continuously supplied with electricity or it may be hooked up to the power supply after the component is attached. In either instance, the component suddenly goes from an initial condition without any power to a condition wherein full power is applied. This occurs when the component is attached to the connector if the conveyor is constantly charged, whereas if the electricity is supplied to the connector after attachment of the component, the power surge occurs when the connector communicates with the power source. This sudden change in power level can result in rather sharp voltage spikes across the circuitry of the component, possibly damaging the circuit. Similarly, a sudden drop in power occurs when the component has completed the testing, either when the component is removed or when the power supply to the connector is terminated. Since this power drop also may harm the circuit, a faulty component may be installed because it has already passed the quality test and is presumed to be reliable.
The electrical supply system in these ovens commonly comprises a pair of long wires or bus bars, with one being positively charged and the other being negatively charged, which contact the electrical connector as it proceeds along the oven with the component. The wires generally extend along substantially the entire length of the oven and are connected to a single power source. If the power source or either of the wires fail, electricity cannot be supplied to the component for testing. This precludes the performance of any quality checks, resulting in the inability to even spot check a batch of components unless a lower capacity back-up testing oven is supplied; thus, faulty components may go undetected.
Accordingly, it would be desirable to have a compact, efficient electronic component testing oven which minimizes thermal shock to the components. It would also be desirable to provide such an oven with an electrical supply which avoids sharp power surges applied to the components and is provided with a back-up system to increase reliability and minimize down time due to failure of a part of the electrical system.